Does the purchase of a mobility scooter alter physical activity levels in older adults?

Purpose: This cohort study investigated changes in physical activity, community mobility and social participation following the first-time purchase of a mobility scooter.Methods: A national sample of persons aged 65+ years was surveyed using customized semi-structured interviews that explored changes in physical activity via the International Physical Activity Questionnaire modified for the elderly, and community involvement. Participants were recruited at the point of purchase of their first mobility scooter, and interviewed at this time and again at 2 and 6 months post-purchase.Results: Eighteen participants (F = 10, M = 8) aged between 65 and 95 years were recruited. Physical activity levels remained unchanged in 12 participants, and declined by at least one category in five participants. All participants reported improvement to their self-perceived quality of life following acquisition of a mobility scooter. Participants did not access additional forms of physical activity, though nine reported increased social participation. At baseline, five participants stated that the scooter was used for journeys they formerly made by other motorized transport, and by the 6-month interview, this number had risen to 15 participants.Conclusions: It is unlikely that changes in physical activity were related to the ageing process given the relatively short time span of the study. Thus it can be inferred that participants viewed their mobility scooter as a vehicle for maintaining their lifestyle rather than as a means to seek out additional activities. Improvements to perceived quality of life may be attributed to continuing or furthering community and social engagement, and a sense of retained independence.Implications for rehabilitationAn awareness of possible changes in physical activity associated with the purchase of a mobility scooter is needed.The purchase of a mobility scooter provides a viable means of transport to facilitate access to physical activity situations.Over-reliance on a mobility scooter has the potential to decrease health-related physical activity.The development and dissemination of a targeted health message about maintaining (or improving) physical activity levels is warranted to increase the awareness in this growing group of new, and current, mobility scooter riders in an increasingly ageing population.

A biopsychosocial understanding of lower back pain: Content analysis of online information.

OBJECTIVES: (1) To develop a checklist to assess the representation of biopsychosocial lower back pain (LBP) online information; (2) to analyse publicly accessed online LBP information from a Google search for the degree that psychosocial contributors are described alongside the traditional biomedical approach to explaining LBP; (3) whether websites use information on pain biology to educate on LBP; (4) any inaccurate or false information regarding the mechanisms of LBP and; (5) the amount of websites certified by established benchmarks for quality health information. MATERIALS AND METHODS: An online search was conducted using the Google search engines of six major English-speaking countries. Website content was analysed using three checklists developed for the purpose of this study - Biopsychosocial information categorisation checklist and scoring criteria; pain biology information checklist; and the inaccurate information checklist. Website quality was identified by the presence of an Health on the Net certification (HONcode). RESULTS: Of the fifteen websites analysed, the content of 26.7% of websites was classified as 'biomedical', 60% 'limited psychosocial' and 13.3% 'reasonable psychosocial'; 20% included information on pain biology; 46.7% inaccurately implied pain to be equal to tissue damage and 46.7% implied pathways specific to pain transmission; 40% were HONcode certified. CONCLUSION: Online LBP information retrieved through a Google search has limited to no integration of psychosocial or pain biology information. The focus on tissue pathology is further supported by the inaccurate descriptions of pain as equal to tissue damage and as an input to the central nervous system (CNS). Online LBP information needs to be guided by criteria more sensitive to the psychosocial contributors to pain. SIGNIFICANCE: The online LBP information retrieved from a Google search needs to be guided by information more sensitive to the psychosocial contributors to pain and disability. This study also highlights the presence of inaccurate information that implied pain as a measure of tissue damage or as an input to the nervous system.

Do post-concussion-like symptom responses change following exercise or sports participation in a non-concussed cohort?

The purposes of this study were (a) to determine the reliable change in post-concussion-like symptoms reported following self-selected exercise or sports activities and (b) to explore the potential influence of gender and exercise parameters on post-concussion-like symptoms reported by a non-concussed cohort following exercise/training. A pre-to-post observational design was used. A convenience sample of students aged 18-30 years who visited a university recreation center to engage in their chosen exercise activity and a purposeful sample of men's and women's rugby union players engaged in their regular training sessions were included in the study. All participants reported their symptoms using the symptom scale of the Sport Concussion Assessment Tool 2. The reliable change index was used to determine the change in symptom scores reported from pre-to post-exercise/training. Multiple linear regression analysis was used to model the exercise variables to explain the impact on the reporting of symptoms. A total of 260 participants (146 males and 114 females) completed their self-selected exercise activity or rugby union training. Approximately two-thirds of all participants did not demonstrate a change (increase or decrease) in total symptom score (201/260, 77.9%) and/or symptom severity score (212/260, 81.9%) from pre-to post-exercise/training. The symptom response following exercise or sports training did not change in the majority of participants. Clinicians need to be aware of these findings to make informed decisions on return-to-play following a concussive brain injury.

Toddlers' Differential Susceptibility to the Effects of Coparenting on Social-Emotional Adjustment.

The present study tested whether infants high in negative affectivity are differentially susceptible to observed coparenting behavior in relation to their subsequent social-emotional development. Data came from a longitudinal study of 182 U.S. dual-earner, primiparous couples and their infant children. At 9-months postpartum, child negative affectivity was reported by mothers and fathers and supportive and undermining coparenting behavior were assessed from mother-father-infant observations. At 27-months mothers reported on toddlers' externalizing behavior and dysregulation using a clinical assessment tool designed to identify competencies and areas of concern in toddlers' social-emotional development. Hierarchical regression analyses revealed partial support for the differential susceptibility hypothesis. Specifically, infants high in negative affectivity had lower levels of dysregulation when embedded in a more supportive coparenting context, and higher levels of dysregulation when embedded in a less supportive coparenting context. In contrast, supportive coparenting behavior was not relevant for the dysregulation of infants initially low in negative affectivity.

Reliability and diagnostic characteristics of clinical tests of upper limb motor function.

There is a paucity of information on the inter-rater reliability and predictive value of components of the neurological examination. Selected tests of upper limb motor function were studied in 34 patients with Parkinson's disease, upper motor neuron disease or cerebellar disease and in 25 control participants. Video recordings were independently evaluated and scored by two clinicians to determine inter-rater reliability (kappa) and predictive values. Kappa values ranged from 0.00 to 0.73. Highest positive predictive values (PPV) were obtained for the Barré test, arm raise, forearm rolling and finger nose tests. Negative predictive values (NPV) were mostly low, with highest values for unimanual sequential finger tap and rhythmic tap. The combined tests had PPV of 0.58 and NPV of 0.73. This study demonstrates that these clinical tests have poor inter-rater reliability and low negative predictive value when used in isolation.

The diagnostic accuracy of selected neurological tests.

The diagnostic value and reliability of selected neurological clinical tests was studied in control subjects with normal neuroimaging (n=42), and subjects with a focal brain lesion (n=38). The items were studied by two examiners blinded to group membership and using standardized protocols, and subsequently by a neurologist who was not blinded to diagnosis. The positive likelihood ratios ranged from 1.06 (pronator drift) to 22.11 (single leg stance with eyes open, while the negative likelihood ratios ranged from 0.47 (tandem gait) to 0.97 (pupil symmetry). Three items (single leg stance - eyes closed - firm surface; single leg stance - eyes open - foam surface; and tandem gait) successfully distinguished between the two groups (odds ratio p<0.05). The inter-rater reliability was generally poor, with only tandem gait showing excellent agreement (kappa [K]=0.92). Tandem gait was the only item to show noteworthy agreement (K=0.93) between the examiners and the neurologist. The tests varied considerably in their ability to detect radiologically demonstrated structural brain lesions, and several items were poorly reproducible, questioning their value as part of a routine neurological examination.

Sports concussion assessment: the effect of exercise on dynamic and static balance.

This study determined the effect of exercise on measures of static and dynamic balance used in the assessment of sports-related concussion (SRC). A balanced three-group cross-over randomized design was used with three levels of exercise verified by blood-lactate, heart rate and "perceived-exertion": no exercise/rest (NE), moderate-intensity exercise (ME), and high-intensity exercise (HE). Participants performed two timed balance tasks: tandem gait (TG) and single-leg stance (SLS); pre- and post-exercise and 15 min after exercise. Linear mixed-models with adjusted means and contrasts compared exercise effects. Ninety asymptomatic participants (45♂:45♀) were recruited. When times were contrasted with NE; HE resulted in a significant decrease in SLS (P<0.001) and TG (P<0.001) performance immediately following exercise. Fifteen minutes of recovery improved SLS (P<0.001) and TG (P=0.011) from post-exercise performance. ME caused a significant decrease in performance in SLS (P=0.038) but not TG (P=0.428). No statistically significant change occurred following ME in any tasks after 15-min recovery (SLS P=0.064; TG P=0.495). Test-retest reliability was considerably higher for the dynamic task compared with the static task. The reliability of static and dynamic balance tasks, and the change in performance following exercise, have implications for the immediate assessment of SRC, as these measures are utilized in concussion assessment instruments.

Self-report scales/checklists for the measurement of concussion symptoms: a systematic review.

OBJECTIVE: To identify self-reported sport concussion symptom scales and to describe the psychometric properties of these identified scales. DESIGN: Systematic review. INTERVENTION: PubMed, Medline, CINAHL, Scopus, Web of Science, Sport Discus, PsycINFO and AMED were searched from their establishment until December 2008. The medical subject heading terms "brain concussion", "signs or symptoms" and "athletic injuries". The search was limited to articles published in English. An additional search of the reference lists of the retrieved articles was conducted. Only full-text articles were considered for this study and these were retrieved to determine whether they met the inclusion criteria. RESULTS: The initial search resulted in 421 articles, which were reduced to 290 articles after removing duplicates. The hand search resulted in 17 articles, thus giving a total of 307 articles. Full text was available for 295 articles of which 60 met the criteria for inclusion. The excluded 235 articles were case reports, reviews and guidelines on concussion management or studies that had not used a symptom scale or checklist. CONCLUSIONS: Six core scales were identified with a broad range of symptom items but with limited information on their psychometric properties. There were numerous derivative scales reported, most of which have not been methodically developed or subjected to scientific scrutiny. Despite this, they do make a contribution to the detection, assessment and return to play decisions but there is a need for the clinical user to be aware that many of these scales have "evolved" rather than being scientifically developed.

Training habits and injuries of masters' level football players: a preliminary report.

OBJECTIVE: To profile training habits and injuries in football players participating in a national Masters tournament. METHODS: A cross-sectional retrospective study design was used to survey male football players attending the 2008 New Zealand Masters Games. Information regarding player demographics, football injuries, football related training, and risk factors for injury were collected. RESULTS: 199 Players were recruited, with a median age of 44 yrs (range 35-73) and a median football playing history of 15 yrs (range 0-66). Irrespective of age, 112 (84%) players included a warm-up and 104 (78%) included a stretching regime in their regular training programme. In the 12 months prior to the tournament, 128 football related injuries were reported by 93 players (64 injuries/100 players or 46 injured players/100 players). The most frequently injured region was the lower limb; specifically the lower leg (n=23), ankle (n=18), hamstring (n=17), knee (n=15), and Achilles tendon (n=15). CONCLUSION: This study provides a preliminary insight into the training habits and injury profiles of Masters football players. Despite all players including some form of injury prevention strategy in their training, a significant number of players experienced an injury in the 12 months prior to the tournament.

The effect of exercise on motor performance tasks used in the neurological assessment of sports-related concussion.

Sports-related concussion is assessed using both cognitive and motor performance tasks. There is limited understanding of how exercise affects these measures. The purpose of this study was to investigate the effect of moderate-intensity exercise on three selected measures of motor performance. A repeated measures design was used to compare baseline motor performance scores with post-exercise scores with an exercise intervention modelled on the physiological demands of a team sport. 30 physically active subjects performed timed motor performance tasks: Finger-to-Nose (FTN), Tandem Gait (TG) and Single Leg Stance (SLS). The tasks were administered twice pre-exercise and twice post-exercise. FTN, TG and SLS demonstrated high test-retest reliability (ICC values >0.8). 15 minutes of moderate-intensity exercise caused a significant improvement in FTN (T2 = 2.66 (SD 0.38), T3 = 2.49 (0.32); p<0.001) and TG (T2 = 13.08 (2.84), T3 = 12.23 (2.22); p = 0.001), but not in SLS (T2 = 5.94 (4.99), T3 = 5.91 (5.54); p = 0.507). Improvement in the performance of motor tasks after exercise has implications for the immediate assessment of sports-related concussion, given that measures of motor performance are utilised in concussion assessment instruments.

Physiotherapists' use of information in identifying a concussion: an extended Delphi approach.

OBJECTIVE: To determine the relative importance of signs and symptoms that a selected cohort of sports physiotherapists use to identify a sports concussion. METHODS: A two-round Delphi methodology was used to achieve consensus in a cohort of 21 sports physiotherapists. A subsequent round involving an educational intervention provided the participants with an opportunity to modify their knowledge base through the provision of a relevant resource article. RESULTS: Participants provided 123 responses, which were grouped into eight descriptive categories with consensus (>80%) being reached for the importance of: cognition/orientation, memory, motor dysfunction and state of consciousness. The category "state of consciousness" remained the most important information source at the completion of the study. CONCLUSION: Participants placed considerable importance on the player's level of consciousness in their decision making. This would appear to be in conflict with recent trends to place greater importance on the role of symptoms in identifying a concussion.

The reliability of H-reflex recordings in standing subjects.

OBJECTIVE: Several studies have used the H-reflex to investigate the effect of upright stances and locomotion on spinal reflex excitability. The reliability of eliciting this reflex during weight-bearing has however yet to be addressed. This study was undertaken to determine the reliability of individual differences in the H-reflex recorded from healthy subjects during quiet standing. Secondary aims of the study were to evaluate individual reliability during prolonged standing, and to establish the minimum number of trials required to provide reliable measurements of the H-reflex. DESIGN AND PARTICIPANTS: Twenty neurologically healthy volunteers participated in a repeated measures design consisting of 8 blocks of 20 trials evenly distributed over two testing sessions. H-reflex recordings were elicited from the subject's dominant side soleus muscle by percutaneously stimulating the posterior tibial nerve. Stimuli were presented every 10 s, with 2 min seated rest provided between blocks of trials. Peak-to-peak amplitude of H-reflexes and m-responses determined for individual trials were used for subsequent analysis. RESULTS: It was found that the reliability of measuring the H-reflex and m-response during quiet standing was extremely robust (r = .97 for both measures). This pattern of individual differences remained consistent over 80 trials confirming the stability of the measures. High reliabilities (r = .96 and .87 for the H-reflex and m-responses respectively) were also observed when as few as four trials were analysed. When measures obtained during the first session of testing were compared with those obtained for session two, the correlation coefficients were generally of a lower order (r = .54 to .90). DISCUSSION: The results demonstrate that the H-reflex in quiet standing provides high intra-individual reliability, suggestive of a stable reflex resistant to potentially confounding postural influences, or other sources of biological variation. The between-session reliability underscores the difficulty in reproducing conditions between sessions, and emphasises the need for within-session comparisons of H-reflex amplitudes. Given the functional challenge of maintaining an upright posture, the H-reflex appears to be a well maintained and stable phenomenon.

The effect of coculture with nonparenchymal cells on porcine hepatocyte function.

Porcine hepatocytes are currently being investigated as a therapy for patients suffering from acute liver failure. Incorporating hepatocytes in an extracorporeal device that would stabilize a patient until transplantation or recovery could dramatically decrease the mortality rate associated with this disease. The ability to maximize hepatocyte function would contribute significantly to being able to provide the required cell mass in a device of reasonable size. Several approaches have been effective at increasing rat hepatocyte function in vitro, including coculture with nonparenchymal cells. In this study, we investigated the effect of the addition of 3T3 cells to porcine hepatocyte culture and found that while there was an increase in albumin secretion, there was little or no effect on urea synthesis or cytochrome P450 activity.

Evaluation of the porcine intestinal collagen layer as a biomaterial.

The submucosal layer of the small intestine has been investigated as a source of collagenous tissue with the potential to be used as a biomaterial because of its inherent strength and biocompatibility. In this study we utilized a novel method for processing the tissue to generate an acellular intestinal collagen layer (ICL). This nondetergent, nonenzymatic chemical cleaning protocol removes cells and cellular debris without damaging the native collagen structure. Multilayer laminates of ICL crosslinked with a water-soluble carbodiimide (EDC) were evaluated as a tissue repair material in a rabbit abdominal hernia model. The ICL laminates provided the requisite physical properties and did not lead to adhesion formation. No immune response to the porcine collagen was detectable, and this material did not show any calcification in either the rabbit model or in the juvenile rat model.

In vitro characterization of porcine hepatocyte function.

The clinical consequences of acute liver failure are associated with high mortality. Intensive medical intervention is required to treat the symptoms of liver failure, including coagulopathy, metabolic instability, and encephalopathy. Providing temporary liver support with an extracorporeal liver assist device could stabilize the patient until a donor liver became available or the patient's own liver was able to recover. The use of human hepatocytes as the biologic component of the assist device is precluded by the scarcity of available tissue and the limited proliferative potential of adult hepatocytes in vitro. Consequently, porcine hepatocytes are being evaluated as a cell source for liver assist devices. Maintaining differentiated function in isolated hepatocytes, however, remains a challenge in the development of this technology and is complicated by the fact that the key therapeutic functions for short-term survival have not been well defined. Several approaches have been effective in prolonging rodent hepatocyte function in vitro, including manipulation of extracellular matrix. Here, we have investigated porcine hepatocyte function in vitro with a specific emphasis on the response to exogenous collagen matrix. In control cultures, albumin secretion increased during the first 7-10 days of culture to an average of 50 +/- 17 microg/day/10(6) cells and then decreased over the next 2 weeks. The pattern of urea synthesis was slightly different in that it was highest in the first 1-3 days postisolation (140 +/- 19 microg/day/10(6) cells) and then decreased by about 50% to a plateau level that was stable during the next 3-4 weeks of culture. Cytochrome P450-mediated activities were the most labile with time in culture and were undetectable after the first week in the absence of pharmacological inducers. In contrast to results reported for rat cells, porcine hepatocytes exhibited differentiated function in the absence of any modification of the culture dish surface and function was not increased or prolonged in the presence of exogenous collagen.

The identification by physiotherapists of the physical problems resulting from a mild traumatic brain injury.

In New Zealand, over 9000 people are diagnosed with a traumatic brain injury (TBI) each year, with at least 80% being classified as mild. The cognitive deficits resulting from mild traumatic brain injury (MTBI) have been well documented, but this is not the case for the physical problems. As a result, the physical problems are not well understood and few people with a MTBI are referred for physiotherapy. The aim of this research was to use a modified Delphi Technique to gain consensus amongst physiotherapists working with TBI clients with regard to: (1) The common motor performance problems associated with MTBI; (2) The importance of assessing these motor performance problem; and (3) Whether these motor performance problems should be used in a formal assessment (FA) or included as a screening measure (SM). Following a pilot study to establish face validity and clarity of instructions, a national sample of 52 physiotherapists with a minimum of 1 year's experience working with TBI clients was recruited. In Round 1, 42 physiotherapists listed 424 physical problems which, in their clinical experience, may occur in people with a recent MTBI. A planning committee developed these listed problems into 33 items. In Round 2, these items were then rated by the physiotherapists as to their importance of being included in an assessment. Using 75% consensus criteria, 31 items were deemed as being at least 'important' for inclusion. In Round 3, the physiotherapists were asked whether these items should be used in a FA or used as a SM. Of the 31 items which were retained, seven reached consensus for FA (balance with unstable, reduced or changing base of support; dynamic standing balance; high level balance activities; quality of movement; ballistic activities; gait; proprioception). Five items reached consensus for being used as a SM (attention; behaviour; sport and leisure activities; vocational activities; quality of movement). Consensus of classification was not reached for the remaining 19 items which had previously been identified in Round 2 as being at least 'important' to be assessed. These results form the foundation for the development of an assessment/management protocol for physiotherapists working with adults with MTBI.

Do cutaneous receptors contribute to the changes in the amplitude of the H-reflex during massage?

Massage is known to produce a reduction in spinal reflex excitability. However, the mechanisms subserving this phenomenon have yet to be elucidated. This study was undertaken to determine the role of superficial cutaneoreceptors overlying the triceps surae during the application of a massage. Twelve neurologically healthy volunteers were subjected to an interrupted repeated measures design consisting of eight conditions. Each condition was comprised of eleven H-reflex recordings obtained from the right soleus muscle. Six conditions served to establish baseline control levels, while the remaining two conditions consisted of reflex recordings obtained simultaneous to the application of the massage. During the first massage condition, subjects were at rest while a three minute petrissage was applied to the right triceps surae muscle group. The second massage condition was always preceded by the application of a topical anaesthetic to abolish the sensation to touch and pin-prick to the skin area that was to be massaged. It was expected that the cutaneous afferents would not play any major role in the changes associated with the application of the massage. H-reflex amplitudes recorded during each massage condition (1.20 mV +/- 0.30 SEM, 1.05 mV +/- 0.23 SEM, respectively) were significantly reduced (F7.77 = 26.048, p < 0.01) in contrast to all control conditions (range: 2.21 to 2.63 mV). However, no difference was observed between the two massage conditions. The inhibitory effects of massage on the soleus H-reflex do not appear to originate from mechanical stimulation of cutaneous mechanoreceptors. It seems more likely that deep mechanoreceptors are involved.

Oxygen consumption characteristics of porcine hepatocytes.

Oxygen uptake rate (OUR) of hepatocytes is an important parameter for the design of bioartificial liver assist (BAL) devices. Porcine hepatocytes were cultured in a specially constructed measurement chamber with an incorporated mixing system and a Clark polarographic oxygen electrode. Signal noise associated with conventional Clark electrode implementations was circumvented by the combination of real time digital numerical averaging and subsequent finite impulse response (FIR) spectral filtering. Additional software allowed for the automated generation of cellular oxygen consumption coefficients, namely, Vmax and K0.5, adding a high degree of objectivity to parameter determination. Optimization of the above numerical techniques identified a 0.1 Hz/200 data point sample size and a 0.004 Hz cutoff frequency as ideal parameters. Vmax values obtained for porcine hepatocytes during the first two weeks of culture showed a maximal consumption of 0.9 nmole/sec/10(6) cells occurring on Day 4 post seeding, and a gradual decrease to 0.31 nmole/sec/10(6) cells by Day 15. K0.5 values increased from 2 mm Hg on Day 2 to 8 mm Hg by Day 8, with gradual subsequent decrease to 4 mm Hg by Day 15. The Vmax and K0.5 values measured for porcine cells were higher than maximal values for rat hepatocytes (Vmax: 0.43 nmole/sec/10(6) cells, K0.5: 5.6 mmHg) and thus may necessitate significantly altered BAL device design conditions to ensure no oxygen limitations. Finally, these results highlight the need for species specific characterization of cellular function for optimal BAL device implementations.

Motor performance following a mild traumatic brain injury in children: an exploratory study.

Mild Traumatic Brain Injury (TBI) is a common occurrence in the paediatric population and, as the concept of motor performance has not been assessed specifically in this population, the purpose of this study was to determine if motor performance deficits are present and can be objectively identified in a sample of children having sustained a mild TBI (Glasgow Coma Scale score 13-15). Twenty-eight children aged between 5 and 15 years were recruited immediately post-trauma. Subjects were considered normal on standard neurological exam at the time of discharge. They were assessed 13-18 days post-trauma using the Bruininks-Oseretsky Test of Motor Proficiency, a norm referenced clinical standardized assessment tool. Compared to published norms, motor performance was significantly lower in domains of balance, response speed and running speed an agility (t-test p < 0.01), and significantly higher in domains of upper extremity coordination and visual motor control (t-test p < 0.01). Although excellent performance can be observed in domains requiring upper limb coordination, motor planning and execution of motor tasks, deficits in balance and response speed can be identified in a significant number of children even after mild TBI. More specific and sensitive evaluations are necessary to identify the exact nature of the problems and evaluate their functional impact on daily activities.

Genomic instability and catalase gene amplification induced by chronic exposure to oxidative stress.

Chronic exposure (>200 days) of HA1 fibroblasts to increasing concentrations of H2O2 or O2 results in the development of a stable oxidative stress-resistant phenotype characterized by increased cellular antioxidant levels, particularly catalase (D. R. Spitz et al, Arch. Biochem. Biophys., 279: 249-260, 1990; D. R. Spitz et al., Arch. Biochem. Biophys., 292: 221-227, 1992; S. J. Sullivan et al., Am. J. Physiol. (Lung Cell. Mol. Physiol.), 262: L748-L756, 1992). Acutely stressed cells failed to develop a stably resistant phenotype or increased catalase activity, suggesting that chronic exposure is required for the development of this phenotype. This study investigates the mechanism underlying increased catalase activity in the H2O2- and O2-resistant cell lines. In H2O2- and O2-resistant cells, catalase activity was found to be 20-30-fold higher than that in the parental HA1 cells and correlated with increased immunoreactive catalase protein and steady-state catalase mRNA levels. Resistant cell lines also demonstrated a 4-6-fold increase in catalase gene copy number by Southern blot analysis, which is indicative of gene amplification. Chromosome banding and in situ hybridization studies identified a single amplified catalase gene site located on a rearranged chromosome with banding similarities to Z-4 in the hamster fibroblast karyotype. Simultaneous in situ hybridization with a Z-4-specific adenine phosphoribosyltransferase (APRT) gene revealed that the amplified catalase genes were located proximate to APRT on the same chromosome in all resistant cells. In contrast, HA1 cells contained only single copies of the catalase gene that were not located on APRT-containing chromosomes, indicating that amplification is associated with a chromosomal rearrangement possibly involving Z-4. The fact that chronic exposure of HA1 cells to either HO2 or 95% O2 resulted in gene amplification suggests that gene amplification represents a generalized response to oxidative stress, contributing to the development of resistant phenotypes. These results support the hypothesis that chronic exposure to endogenous metabolic or exogenous environmental oxidative stress represents an important factor contributing to gene amplification and genomic instability.